Optimization and quantitative characterization of mannitol production by Limosilactobacillus fermentum for functional mango juice application

Abstract

In situ bioconversion of fructose to mannitol by heterofermentative lactic acid bacteria is a promising strategy for developing low-sugar, mannitol-enriched fruit beverages. In this study, a high mannitol-producing isolate, designated 35-12, was isolated from the fermentation broth of traditional fermented bamboo shoots and taxonomically assigned to Limosilactobacillus fermentum based on colony morphology, Gram staining, and 16S rDNA phylogenetic analysis. In artificial medium, fermentation parameters were optimized as 100 g/L total sugar with a glucose-to-fructose (G:F) mass ratio of 1:2, initial pH 6.5, and fermentation temperature of 37 ℃. Under these conditions, the maximum mannitol yield reached 59.41 ± 0.08 g/L. To evaluate matrix-dependent bioconversion performance, strain 35-12 was further tested in different 10-fold diluted NFC juice matrices, among which mango juice showed the highest mannitol production. In the unadjusted diluted mango-juice-based matrix (initial pH 3.91), fructose decreased from 13.40 ± 0.20 to 7.54 ± 0.16 g/L after 72 h, while 5.22 ± 0.14 g/L mannitol was generated in situ, corresponding to an apparent fructose-to-mannitol conversion rate of 89.13 ± 3.81%. Detectable intracellular mannitol dehydrogenase activity was also retained under the naturally acidic mango juice condition, supporting continued fructose-to-mannitol conversion in this complex matrix. These findings provide laboratory-scale evidence for a pH-adjustment-free in situ fructose-to-mannitol bioconversion strategy in a diluted acidic mango juice matrix and support further development of low-sugar, mannitol-enriched fermented fruit beverages.